Replace PHP short tags

Co-authored-by: LeOSW42 <673670+LeOSW42@users.noreply.github.com>

third/Md/Markdown.php

@@ -456,7 +456,7 @@ class Markdown implements MarkdownInterface {
 					[ ]*
 					(?=\n{2,}|\Z)		# followed by a blank line or end of document
 
-			| # PHP and ASP-style processor instructions (<? and <%)
+			| # PHP and ASP-style processor instructions (<?php and <%)
 
 					[ ]{0,'.$less_than_tab.'}
 					(?s: